選擇排序（Selection-Sort）
先把最小的拿出來
剩下的， 再把最小的拿出來
剩下的， 再把最小的拿出來
。。。
每次選擇還沒處理的元素里最小的元素
選擇排序就是重復(fù)“從待排序的數(shù)據(jù)中尋找最小值，將其與序列最左邊的數(shù)字進(jìn)行交換”這一操作的算法。在序列中尋找最小值時(shí)使用的是線性查找。
比如: 對數(shù)字1~9進(jìn)行排序。 使用線性查找在數(shù)據(jù)中尋找最小值，于是我們找到了最小值 1
- 一層版
#include <iostream>
using namespace std;
int main(){
int arr[] = {6, 1, 7, 8, 9, 3, 5, 4, 2};
int len = sizeof(arr)/sizeof(arr[0]);
int minIndex = 0;
for (int j = 0; j < len; ++j) {
if (arr[j] < arr[minIndex])
minIndex = j;
}
cout<<"minIndex = "<< minIndex <<endl;
// 交換
int temp = arr[0];
arr[0] = arr[minIndex];
arr[minIndex] = temp;
for (int i = 0; i < len; ++i)
cout<<arr[i]<<"\t";
cout<<endl;
cout<<"-------------------------------"<<endl;
cout<<"-------------------------------"<<endl;
minIndex = 1;
for (int j = 1; j < len; ++j) {
if (arr[j] < arr[minIndex])
minIndex = j;
}
cout<<"minIndex = "<< minIndex <<endl;
// 交換
temp = arr[1];
arr[1] = arr[minIndex];
arr[minIndex] = temp;
for (int i = 0; i < len; ++i)
cout<<arr[i]<<"\t";
cout<<endl;
cout<<"-------------------------------"<<endl;
cout<<"-------------------------------"<<endl;
minIndex = 2;
for (int j = 2; j < len; ++j) {
if (arr[j] < arr[minIndex])
minIndex = j;
}
cout<<"minIndex = "<< minIndex <<endl;
// 交換
temp = arr[2];
arr[2] = arr[minIndex];
arr[minIndex] = temp;
for (int i = 0; i < len; ++i)
cout<<arr[i]<<"\t";
cout<<endl;
cout<<"-------------------------------"<<endl;
cout<<"-------------------------------"<<endl;
}
在這里插入圖片描述
最終版
#include <iostream>
using namespace std;
int main(){
int arr[] = { 6, 1, 7, 8, 9, 3, 5, 4, 2};
int len = sizeof(arr)/sizeof(arr[0]);
for (int i = 0; i < len - 1; ++i) {
int minIndex = i;
for (int j = i; j < len; ++j) {
if(arr[j] < arr[minIndex])
minIndex = j;
}
// 小優(yōu)化
if (minIndex != i){
int temp = arr[i];
arr[i] = arr[minIndex];
arr[minIndex] = temp;
}
}
for (int i = 0; i < len; ++i) {
cout << arr[i] <<"\t";
}
cout <<endl;
}
在這里插入圖片描述
二維數(shù)組
int main(){
const int M= 3, N=4;
int arr[M][N] = {1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12};
// 遍歷 二維矩陣
for (int i = 0; i < M; ++i) {
for(int j = 0; j < N; j++){
cout << arr[i][j] <<"\t";
}
cout <<endl;
}
}
二維數(shù)組的定義方式
1. 數(shù)據(jù)類型 數(shù)組名[行數(shù)][列數(shù)];
2. 數(shù)據(jù)類型 數(shù)組名[行數(shù)][列數(shù)] = {{數(shù)據(jù)1, 數(shù)據(jù)2...}, ..... {數(shù)據(jù)n, 數(shù)據(jù)n+1}....};
3. 數(shù)據(jù)類型 數(shù)組名[行數(shù)][列數(shù)] = {數(shù)據(jù)1, 數(shù)據(jù)2, ......};
4. 數(shù)據(jù)類型 數(shù)組名[][列數(shù)] = {數(shù)據(jù)1, 數(shù)據(jù)2, ......};
可以省略行, 不可以省略列
#include <iostream>
using namespace std;
int main() {
// 1. 數(shù)據(jù)類型 數(shù)組名[行數(shù)][列數(shù)];
int arr[2][3];
// 沒有賦值時(shí), 數(shù)組中的變量是不確定的
for (int i = 0; i < 2; ++i) {
for (int j = 0; j < 3; ++j) {
cout << arr[i][j] << "\t"; //第 i 行 第 j 列
}
cout << endl;
}
arr[0][0] = 1;
arr[0][1] = 2;
arr[0][2] = 3;
arr[1][0] = 4;
arr[1][1] = 5;
arr[1][2] = 6;
for (int i = 0; i < 2; ++i) {
for (int j = 0; j < 3; ++j) {
cout << arr[i][j] << "\t"; //第 i 行 第 j 列
}
cout << endl;
}
// 2. 數(shù)據(jù)類型 數(shù)組名[行數(shù)][列數(shù)] = {{數(shù)據(jù)1, 數(shù)據(jù)2...}, ..... {數(shù)據(jù)n, 數(shù)據(jù)n+1}....};
cout << "====================================" << endl;
int arr2[2][3] = {{1, 2, 3},
{4, 5, 6}};
for (int i = 0; i < 2; ++i) {
for (int j = 0; j < 3; ++j) {
cout << arr2[i][j] << "\t"; //第 i 行 第 j 列
}
cout << endl;
}
// 3. 數(shù)據(jù)類型 數(shù)組名[行數(shù)][列數(shù)] = {數(shù)據(jù)1, 數(shù)據(jù)2, ......};
cout << "====================================" << endl;
int arr3[2][3] = {1, 2, 3, 4, 5, 6};
for (int i = 0; i < 2; ++i) {
for (int j = 0; j < 3; ++j) {
cout << arr3[i][j] << "\t"; //第 i 行 第 j 列
}
cout << endl;
}
// 4. 數(shù)據(jù)類型 數(shù)組名[][列數(shù)] = {數(shù)據(jù)1, 數(shù)據(jù)2, ......};
cout << "====================================" << endl;
int arr4[][3] = {1, 2, 3, 4, 5, 6};
for (int i = 0; i < 2; ++i) {
for (int j = 0; j < 3; ++j) {
cout << arr4[i][j] << "\t"; //第 i 行 第 j 列
}
cout << endl;
}
}
?維數(shù)組數(shù)組名
- 查看?維數(shù)組所占內(nèi)存空間
- 獲取?維數(shù)組?地址
#include <iostream>
using namespace std;
int main(){
const int M= 3, N=4;
int arr[M][N] = {1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12};
cout <<"arr total size = "<<sizeof(arr)<<endl;
cout <<"arr include elements = "<<sizeof(arr)/sizeof(arr[0][0])<<endl;
cout <<"row total size = "<<sizeof(arr[0])<<endl;
cout <<"row total size = "<<sizeof(arr[1])<<endl;
cout <<"row include elements = "<<sizeof(arr[1])/sizeof(arr[0][0])<<endl;
// 數(shù)組名存儲的是首地址
cout <<"arr = "<<arr<<endl; // 0x7ffee103e910
cout <<"arr = "<<&arr[0][0]<<endl; // 0x7ffee103e910 &變量名 是取出變量的地址
cout <<"arr = "<<&arr[0][1]<<endl; // 0x7ffee103e910
cout <<"arr = "<<&arr[0][2]<<endl; // 0x7ffeeaecd914
cout <<"arr = "<<&arr[0][3]<<endl; // 0x7ffeeaecd918
cout <<"arr = "<<&arr[1][0]<<endl; // 0x7ffeeaecd91c
cout <<"arr = "<<&arr[1][1]<<endl; // 0x7ffeeaecd920
cout <<"arr = "<<&arr[1][2]<<endl; // 0x7ffeeaecd924
cout <<"arr = "<<&arr[1][3]<<endl; // 0x7ffeeaecd928
}
image
int main(){
// 計(jì)算三名同學(xué)的總成績
int scores[][3] = {{100, 100, 100}, {90, 30, 100}, {60, 70, 80}};
string names[] = {"zhangsan", "lisi", "wangwu"};
for(int i = 0; i< 3; i++){
int sum = 0;
for(int j = 0; j < 3 ; j++){
sum += scores[i][j];
}
cout <<names[i]<<" total scores = "<<sum<<endl;
cout <<names[i]<<" mean scores = "<<sum/3.0<<endl;
}
}
編寫程序?qū)崿F(xiàn)矩陣的轉(zhuǎn)置操作（行變列， 列變行）
#include <iostream>
using namespace std;
int main(){
int X[5][4]={{1, 2, 3, 4}, { 5, 6, 7, 8,}, {9, 10, 11, 12}, {13, 14, 15, 16}, {17, 18, 19, 20}};
int XT[4][5];
cout<< "T before ------------------------------" <<endl;
for (int i = 0; i < 5 ; ++i) {
for (int j = 0; j < 4; ++j) {
cout<<X[i][j]<<"\t";
}
cout<<endl;
}
// 轉(zhuǎn)置
for (int i = 0; i < 5 ; ++i) {
for (int j = 0; j < 4; ++j) {
// 核心 行變列, 列變行
XT[j][i] = X[i][j];
}
}
cout<< "T after ------------------------------" <<endl;
for (int i = 0; i < 4 ; ++i) {
for (int j = 0; j < 5; ++j) {
cout<<XT[i][j]<<"\t";
}
cout<<endl;
}
}
作業(yè)
統(tǒng)計(jì)數(shù)組a和b對應(yīng)位置元素相等的個(gè)數(shù)
int a[3][4]={1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12},
int b[3][4]={12, 2, 3, 4, 10, 6, 7, 11, 9, 5, 8, 1};
